My lappy has started completely freezing (no mouse/key input) but screen staying static. It then won't boot up, but after a while on board diagnostics find ram and hdd as good. It'll then boot, run a bit and hang. Diagnostic thoughts appreciated. Suspecting something thermal.

Yeah, if it's a Toshiba, you need to take it apart and remove the miniscule amount of dust caked on the inside of the undersized heatsink. It's become a biannual ritual for me. Toshiba laptops overheat with just a tiny bit of dust in the heatsink. I'm not sure if other makes have the same issue.

I've found teardown instructions, and it seems to access the heatsink I pretty well have to take it entirely apart. Rather than monoploize a table or two at the shop (and have things wander) I've cleared the floor of my study, and am going to dig into this at home. Will holler with updates